1. Field of the Invention
The present invention relates generally to a method of fabricating an electronic component utilizing a monolithic ceramic body, and more particularly, to a method of fabricating a multilayered type component having an improved process of forming inner electrodes.
2. Description of the Prior Art
Conventionally, a multilayer capacitor has been fabricated through the following processes.
First, ceramic green sheets formed in a sheet shape by the Doctor blade process are prepared. Conductive paste including metal to be inner electrodes, for example, palladium, silver-palladium or nickel is printed in a predetermined pattern on the upper surface of the ceramic green sheet by screen process printing. Generally, large ceramic green sheets are used, and the ceramic green sheets are laminated and then, cut in the later process, to fabricate a plurality of multilayer capacitors. Consequently, the above described conductive paste for forming inner electrodes is printed in a plurality of regions on the upper surface of the ceramic green sheet.
A plurality of ceramic green sheets each having conductive paste printed thereon are laminated and pressed in the direction of thickness. Thereafter, a laminated body obtained by pressing in the above described manner is cut in the direction of thickness so as to obtain laminated bodies to respectively constitute multilayer capacitors.
Each of the laminated bodies obtained is then fired, to obtain a sintered body. Thereafter, conductive paste for outer electrodes is applied and baked in a predetermined region on the surface of the sintered body, thereby to complete a multilayer capacitor.
In order to make the multilayer capacitor much smaller in size and larger in capacitance, the thickness of a ceramic layer between inner electrodes should be reduced.
If the ratio of the thickness of the ceramic layer to the thickness of the inner electrode after firing is made too small, however, a shrinkage of the ceramic layer is controlled by a shrinkage of the conductive paste at the time of firing. As a result, there arises the problem that the sintered body is cracked or the firing shrinkage percentage becomes unstable.
Furthermore, the conductive paste contains a solvent. The ceramic green sheet is swelled, or melted by the solvent. Accordingly, there are also problems of shortcircuiting the inner electrodes and decreasing the withstand voltage.
Therefore, a method of thinning the ceramic layer by using as an inner electrode a metal film obtained by the thin film forming process such as evaporation, sputtering or plating has been proposed. More specifically, the method is one for increasing the reliability in a case where the ceramic layer is thinned by not using relatively thick conductive paste but using a thin inner electrode formed by the thin film forming process.
However, the metal film itself formed by the thin film forming process has a small thickness. Accordingly, some problems are liable to arise. For example, the inner electrode is broken at the time of firing.
More specifically, the sintering temperature of the inner electrode formed by the thin film forming process is lower than that of the conventional inner electrode composed of conductive paste. Consequently, if the ceramic layer is raised to a temperature at which the ceramic layer is considerably sintered, the metal film shrinks, so that the inner electrode is liable to be broken.
In order to prevent the inner electrode from being broken, the alloying process is considered to raise the sintering temperature of metal or improve the wettability between metal and ceramics.
In the thin film forming process, however, it is difficult to form metal of the alloy composition to a thin film without any modification. In many cases, the alloy composition of the thin film formed largely differs from the intentional alloy composition. More specifically, it is very difficult to control the alloy composition. Consequently, it is very difficult to form inner electrodes of the desired alloy composition.